The invention concerns a winding configuration for a cryomagnet with at least one winding section, said section consisting of a parallel connection of a winding made from wire which is superconducting at the operating temperature and a winding made from normally conducting wire.
Such a winding configuration is known in the art from DE-A 35 32 396. This known winding configuration exhibits many winding sections each of which consists of a parallel connection of a winding made from wire which is superconducting at the operating temperature and a winding made from normally conducting wire. The individual windings each form a layer of the winding configuration and two separated layers are connected in parallel to form a winding section. The layers formed from normally conducting windings are composed of copper wire and serve not only the purpose of guaranteeing good quench dispersion, but also function as bindings which prevent an unacceptable stretching of the superconducting wire windings due to tensile stresses occurring in the superconducting wire.
The size of the known winding configuration with the described construction is determined by two factors, namely by the limiting value for the product between the current density and the magnetic field strength, and the cross section of the normally conducting material necessary for current take-over in case of a quench. The cryomagnet winding configuration sizes stemming from these factors impact on the weight, especially in cases involving cryomagnets with large inner diameters such as those used in magnetic resonance imaging. Winding configurations for superconducting tomography magnets achieve a weight on the order of several metric tons, so material costs represent a significant factor in the costs of the winding configuration. Moreover, problems associated with mounting such winding configurations in a cryostat increase with the weight of the winding configuration. Accordingly, measures which allow a reduction in the weight of such winding configurations would abate many problems associated with the construction of cryomagnets and, at the same time, lead to cost savings.
Known in the art from patents DE-A 26 02 735, DE-A 33 29 390 and from the scientific technical journal "IEEE Transactions on Magnetics " MAG -23 (1987), pages 914 through 917, as well as from the article "Large Superconducting Magnets for M.H.D." by Z. J. J. Stekly on pages 112-114 in the Journal "Cryogenic Engineering, The Proceedings of the First Cryogenic Engineering Conference held in Tokyo and Kyoto, Japan on Apr.9-13, 1967", are various ready-made superconductor wires of cables with which winding configurations for cryomagnets can be manufactured. Each of these ready-made wires or cables is so dimensioned as to satisfy the requirements on superconductivity and normal conductivity as well as on mechanical stability. In manufacturing a complete winding configuration for a cryomagnet, each part of the ready-made wire or cable must satisfy the most stringent mechanical requirements occurring within the entire winding configuration since in using these types of ready-made wire or cable, a position dependent variation within the winding structure is not possible. This represents, likewise, a substantial design restriction for the winding configuration in its entirety. Furthermore, these types of ready-made wire are too expensive for the manufacture of winding configurations with large inner diameters such as those needed in tomography magnets.
Various cryomagnet winding configuration structures are known in the art from the technical publication "The Review of Scientific Instruments" 36 (1965), pages 825 through 830. One of the known winding configurations has a foil layer between two respective winding layers, which can be strengthened with a metal mesh. If present, this type of metal mesh strengthened foil located between two counter-wound layers effects a stable mechanical localization of the individual layer windings against each other, such that springing of windings against each other due to the axial forces which occur should be avoided. The avoidance of such a springing of windings is necessary in order to exclude the occurrence of a thereby caused quench release. The metal mesh within the foil is, however, necessarily put into place between the winding layers without being stretched in the circumferential direction and, therefore, does not serve as radial mechanical support for the underlying winding wire.
With respect to this prior art, it is the purpose of the present invention to further develop a winding configuration of the above mentioned kind in such a way that said winding can be economically manufactured with substantially reduced volume.